<!DOCTYPE html>
<html>
  <head>
    <title>Events: submit</title>
    <script src='jquery-1.11.1.min.js'></script>
  </head>
  <body>
    <form id='form'>
      First name: <input id='fname' type='text' name='fname'><br>
      Last name:  <input id='lname' type='text' name='lname'><br>
      <input type='submit'>
    </form>
    <script>
      $('#form').submit(function()
      {
        if ($('#fname').val() == '' ||
            $('#lname').val() == '')
        {
          alert('Please enter both names')
          return false
        }
      })
    </script>
  </body>
</html>
